As is known in the art, there is a requirement in many applications for the active cancellation of large signal interferers in radio frequency (RF) and microwave receivers. Numerous active cancellation schemes based on feed-forward (see for example: S. Ayazian, and R. Gharpurey, “Feedforward interference cancellation in radio receiver front-ends,” IEEE Transactions on Circuits and Systems-II Express Briefs, vol. 54, no. 10, pp. 902-906, October 2007 and H. Darabi, “A blocker filtering technique for SAW-less wireless receivers,” IEEE Journal of Solid State Circuits, vol. 42, no. 12, pp. 2766-2773, December 2007) or feedback (see for example T. Werth, C. Schmits, R. Wunderlich, and S Heinen, “An active feedback interference cancellation technique for blocker filtering in RF receiver front-ends,” IEEE Journal of Solid-State Circuits, vol. 45, no 5, pp. 989-997, May 2010) approaches have been developed, but incorporate a low-noise amplifier (or gain amplifier) in the primary signal path as a means to achieve cancellation. The incorporation of this active component in the primary signal path limits the power handling capabilities of the active cancellation circuitry. Similarly, many approaches only provide active cancellation for continuous wave (CW) signals or modulated/encoded signals based on relatively slow (<1 Mbps) modulation/encoding schemes, and require a finite amount of time for the cancellation to synchronize with the system. The ability to have the cancellation error signal generated and utilized in the cancellation approach within the first period of the interfering signal is highly desirable, as well as the ability to cancel moderate power (>10 dBm) interferers without the use of high-linearity (and high power) LNA's in the primary path.
As is also known in the art, feed-forward active cancellation is based on the ability to generate an error signal that is identical in amplitude and 180 degrees out of phase with the interfering signal, and then combine this error signal with the interfering signal to cancel it out. An approach previously developed is shown in FIG. 1. Here, the input signal (e.g., RF/microwave frequency having both the desired signal and the interfering signal of known radio frequency) is sampled and fed to an auxiliary path. The desired signal and the interfering signal in the auxiliary path are down-converted in frequency with in-phase (I) and quadrature (Q) local oscillator signals (LOI, LOQ) and a pair of mixers, as shown; with the interfering signal being converted to a known intermediate frequency (IF) or baseband frequency. The frequency down-converted signal is then amplified (or attenuated) to achieve the correct amplitude for maximum cancellation. The signal is also sent through a bandpass or lowpass filter, which is tuned to the known IF or baseband frequency, to filter out all other signals (i.e. the desired signal) leaving only the interferer/error signal in the auxiliary path. This remaining interfering signal is then up-converted in frequency by in-phase (I) and quadrature (Q) local oscillator signals (LOI, LOQ) and a pair of mixers, as shown, back to the RF/microwave frequency of interest (i.e., the original known interfering radio frequency) and combined with the full spectrum of the signal in the primary path (i.e., the input signal) to enable cancellation of the interfering signal in the primary path. As shown in FIG. 1, the auxiliary path performs both the frequency down-conversion and up-conversion in a pseudo-Weaver architecture (B. Razavi, “RF Microelectronics”, Upper Saddle River, Prentice Hall, 1998), to address image rejection concerns during up-conversion. Both amplitude alignment and phase alignment of the interfering signal in the primary and auxiliary paths must also be addressed to achieve cancellation, either by minimizing the phase and amplitude variation in the two paths, or by compensating for the variation in the primary path or in the auxiliary path.